The present invention relates generally to microwave waveguide components, and more particularly, to waveguide components that are fabricated from metallized, molded thermoplastic.
For microwave applications, waveguides and waveguide assemblies are generally fabricated from metal. Specific standards for commonly used metallic alloys and standards for configurations regarding rigid rectangular waveguides, including brazing and fabrication methods, are available through the United States National Bureau of Standards. Another source of such information is the American Standards of Test and Materials available through the American Society of Mechanical Engineers (ASME). The most commonly used metallic materials are aluminum alloys (alloy numbers 1100, 6061, and 6063 per ASTM B210 and cast brazable alloys such as 712.0,40E, and D612 per QQ-A-601), magnesium alloy (alloy AZ31B per ASTM B107), copper alloys (per ASTM B372 and MIL-S-13282), silver alloy (grade C per MIL-S-13282), silver-lined copper alloy (grade C per MIL-S-13282), and copper-clad Invar. These materials may be divided into two classes--rigid and flexible. The rigid materials are either wrought, drawn, cast, electroformed, or extruded, while the flexible materials consist of convoluted tubing. If these materials are not formed to net shape, they are either machined to shape (when all features are accessible) or broken down into individual details and joined together to form complex assemblies.
Additional information regarding rigid rectangular waveguides can be found in MIL-W-85G, while rigid straight, 90 degree step twist, and 45-, 60-, and 90-degree E and H plane bend and mitered corner waveguide parameters are given in MIL-W-3970C. ASTM B102 covers magnesium alloy extruded bars, rods, shapes, and tubes. Aluminum alloy drawn seamless tubes and seamless copper and copper-alloy rectangular waveguide tubes are discussed in ASTM B210 and ASTM B372, respectively. Waveguide brazing methods are given in MIL-B-7883B, while electro forming is discussed in MIL-C-14550B. It is in the fabrication of complex shapes that the disadvantages of metallic waveguides become most apparent.
Typically, conventional waveguide components are individually machined metal parts that have a relatively high raw material costs, are relatively heavy, and have a relatively long fabrication time. The metal components have each feature machined one at a time. The RF performance of conventional machined parts, such as dip brazed aluminum assemblies is unpredictable. The high temperatures encountered during the brazing process cause unpredictable distortions in the RF microwave features. This degrades the performance obtained from the finished metal assemblies.
Regarding the existing state of the art in molded thermoplastic waveguide components, reference is made to U.S. Pat. No. 4,499,157, entitled "Solderable Plated Plastic Components and Processes for Manufacture and Soldering," owned by the assignee of the present invention. This patent discloses waveguide components that are fabricated by electroplating molded waveguide components and thereafter assembling them using a tin-lead soldering process.